The invention concerns an arrangement for regulating a spark-ignition internal combustion engine, in particular a stationary boosted gas Otto-cycle engine, comprising a power regulating device acting on at least one power setting member.
An arrangement of that kind is known for example from European patent EP 0 259 382. There, the mixture pressure which prevails upstream of the inlet valves of the internal combustion engine is used as a regulating parameter in order finally to regulate the combustion gas-air ratio. That is directly correlated to the proportions of NOx in the exhaust gas, so that overall this involves an emission regulator in the form of a lambda regulator. The target parameters of that known engine regulating system are therefore power and nitrogen oxide emission NOx. In order to achieve the regulating target the boost pressure and the combustion gas-air ratio lambda are altered. Power and nitrogen oxide emission are coupled to all engine parameters so that the power and emission regulator is generally intercoupled regulators.
Admittedly, such a known regulation strategy makes it possible to regulate the nitrogen oxide emissions to a predetermined value and to hold the power at the desired value. It is however not possible with the known regulation strategy always to implement ongoing optimisation of the level of efficiency because the optimum operating point depends on environmental conditions such as induction temperature, altitude of installation and the quality of fuel gas.
Therefore the object of the present invention is to provide an improved arrangement for regulating a spark-ignition internal combustion engine of the general kind set forth in the opening part of this specification, with which it is always possible to hold an operating point which is the optimum in terms of level of efficiency, even with a fluctuating fuel gas quality and fluctuating environmental conditions. It will be appreciated that in that respect preferably the regulating properties which are already previously known, in regard to a given power and a given (constant) emission of pollutants, in particular NOx, are to be maintained.
In accordance with the invention that is achieved in that there is provided an ignition time regulating device which adjusts the ignition time in dependence on the position of the power setting member. In the case of boosted gas Otto-cycle turbocharged engines the ignition time represents a further engine parameter which permits a variation in the attainable full load by later setting of that time. That makes it possible to implement a regulation function which at any time guarantees a minimum regulation reserve by varying the ignition time. In that way it is possible always to operate at the internal combustion engine operating point which is optimum in terms of the level of efficiency, without running the risk of no longer attaining the required emission values or the required power output in the event of fluctuating environmental conditions or fluctuating fuel gas qualities.
For that purpose it can preferably be provided that the ignition time regulating device has at the input side a threshold value device which limits the ignition time adjustment to positions of the power setting member which are above a pre-settable value and the highest power value of the power setting member. Ignition time regulation therefore remains inactive until the power setting member, for example a blow-off valve in a turbobypass or the throttle flap is just at the position corresponding to maximum power. When the power setting member has reached a predetermined position, for example the blow-off valve is throttled down to 20% of a passage (and the throttle flap is already completely opened), ignition time regulation intervenes by setting the ignition time to later whereby power rises. Then, in regard to the actual power setting member, a regulation reserve is still available, which makes it possible to intervene rapidly in terms of engine power output in the event of fluctuating conditions so that the engine can always maintain its power. The power setting member can do that rapidly in terms of time while ignition time regulation requires only a longer response time. It affords in practice the power reserve for the actual power setting member so that it is always possible to operate at the optimum operating point at the power limit, without having to run the risk of no longer attaining the engine power output, under adverse external conditions.
In addition, by way of incorporating the ignition time into the regulating system, it is possible to prevent the knock or detonation limit from being exceeded. It is therefore also possible to cautiously approach the knock or detonation limit. For that purpose it is preferably provided that the ignition time regulating device has an output signal limiter which ensures that the ignition time is at any event adjustable only between two pre-settable limits in the late direction, and in the early direction, in which respect there is provided a knock regulator which on the input side has at least one knock sensor on the internal combustion engine and which is connected on the output side to the output signal limiter and which when knocking combustion occurs reduces the effective limit for adjustment of the ignition time in the direction early until knocking combustion no longer occurs.
As mentioned in the opening part of this specification, it is already known that it is possible to regulate the combustion gas-air ratio and therewith the levels of pollutant emission (NOx) by way of regulation of the boost pressure in dependence on the parameters consisting of engine power and mixture temperature upstream of the inlet valves. The relationship between the emission reference value or the reference value for the combustion gas-air ratio lambda on the one hand and the boost pressure on the other hand is dependent on ignition time. For that reason, a preferred embodiment provides that this emission regulation also involves the ignition time as a parameter which varies. A preferred embodiment is characterised in that the lambda regulator receives at the actual value input an actual value signal corresponding to the mixture pressure upstream of the valves of the internal combustion engine and at the reference value input there is a reference value signal which is calculated in dependence on a pre-settable reference value for the amount of NOx contained in the exhaust gases and in dependence on the currently detected values in respect of engine power output, the mixture temperature upstream of the valves and the current ignition time.